This invention relates to an information decoding method and device, an information coding method and device, and a providing medium. It particularly relates to an information decoding method and device, an information coding method and device, and a providing medium for restraining output of an unpleasant sound by erasing an aliasing component with respect to a code string formed by coding only a signal of a partial frequency band of acoustic waveform signals.
Conventionally, there are various methods and devices for high efficiency coding of audio or sound signals. For example, such methods and devices can be exemplified by a transform coding system which is adapted for forming frames of signals in the time domain, then converting (spectral conversion) each frame of signals in the time domain to signals in the frequency domain, splitting the signals into a plurality of frequency bands and coding each band of signals, and a so-called subband coding (SBC) system which is adapted for splitting audio signals in the time domain into a plurality of frequency bands and coding each band of signals, without forming frames of audio signals. Also, there is considered a method and device for high efficiency coding using the above-described subband coding in combination with transform coding. In this case, after band splitting is carried out by the subband coding system, each band of signals are spectrally converted to signals in the frequency domain, and coding is carried out on each spectrally converted band.
As a band splitting filter used in the above-described subband coding system, there is employed, for example, a polyphase quadrature filter (PQF), which is described in Joseph H. Rothweiler, xe2x80x9cPolyphase Quadrature Filtersxe2x80x94A new subband coding technique,xe2x80x9d ICASSP 83, BOSTON. This PQF can split a signal into a plurality of bands of equal widths at a time and is characterized in that so-called aliasing is not generated in synthesizing the split bands later.
As the above-described spectral conversion, there is employed spectral conversion for forming frames of input audio signals of predetermined duration and carrying out a discrete Fourier transform (DFT), discrete cosine transform (DCT) or modified discrete cosine transform (MDCT) on each frame so as to convert the time domain to the frequency domain, MDCT is described in J. P. Princen and A. B. Bradley, xe2x80x9cSubband/Transform Coding Using Filter Bank Designs Based on Time Domain Aliasing Cancellation,xe2x80x9d Univ. of Surrey Royal Melbourne Inst. of Tech. ICASSP 1987.
By thus using the filter and spectral conversion to quantize the signals split for each band, the band in which quantization noise is generated can be controlled and coding can be carried out at an auditorily higher efficiency using characteristics such as a so-called masking effect. Also, by normalizing the maximum value of absolute values of signal components for each band before carrying out quantization, coding can be carried out at a higher efficiency.
As a frequency splitting width in quantizing each frequency component (hereinafter referred to as a spectral component) split into frequency bands determined by human auditory characteristics is often employed. Specifically, critical bands whose bandwidths increase as the frequency becomes higher are used to split audio signals into a plurality of bands (for example, 25 bands). In coding each band of data at this point, coding is carried out by using predetermined bit distribution for each band or adaptive bit allocation for each band. For example, in coding coefficient data obtained by MDCT processing by using the foregoing bit allocation, coding is carried out by using an adaptive number of allocated bits with respect to each band of MDCT coefficient data obtained by MDCT processing on each frame.
The following two methods are known as the bit allocation method.
For example, in R. Zelinski and P. Noll, xe2x80x9cAdaptive Transform Coding of Speech Signals,xe2x80x9d IEEE Transactions of Acoustics, Speech, and Signal Processing, Vol.ASSP-25, No.4, August 1977, bit allocation is carried out on the basis of the magnitude of signals of each band. In this method, the quantization noise spectrum becomes flat and the noise energy is minimized. However, since the auditory masking effect is not used, the actual auditory perception of noise is not optimum.
On the other hand, for example, in M. A. Kransner, xe2x80x9cThe critical band coderxe2x80x94digital encoding of the perceptual requirements of the auditory system,xe2x80x9d MIT, ICASSP 1980, there is described a method for obtaining a signal-to-noise ratio required for each band by utilizing auditory masking so as to carry out fixed bit allocation. However, in this method, since bit allocation is fixed, a satisfactory characteristic value cannot be obtained even in the case where characteristics are measured by using a sine wave input.
To solve these problems, a high efficiency coding device is proposed in which all the bits that can be used for bit allocation are divided into bits for a fixed allocation pattern predetermined for each band or each block obtained by subdividing each band and bits for bit distribution dependent on the magnitude of signal frequency components in each subband, and in which the division ratio is caused to depend on signals related to input signals to that the division ratio for the fixed bit allocation pattern is increased as the spectral distribution of the signals becomes smoother.
According to this method, in the case where the energy is concentrated on a specified spectral component as in the case of a sine wave input, the overall signal-to-noise characteristic can be significantly improved by allocating a greater number of bits to a block including that spectral component. In general, the human auditory sense is extremely acute with respect to signals having steep spectral distribution. Therefore, improvement of the signal-to-noise characteristic by using such method is effective not only for improving the numerical value of measurement but also for improving the auditorily perceived sound quality.
In addition to the foregoing method, various other methods are proposed as the bit allocation method. If a model related to the auditory sense is made fine to improve the capability of the information coding device, coding can be carried out at an auditorily higher efficiency.
In the case where the above-described DFT or DCT is used as the method for spectral conversion of waveform signals consisting of waveform elements (sample data) such as digital audio signals of the time domain, blocks are formed by every M units of sample data and spectral conversion of DFT or DCT is carried out on each block. By carrying out spectral conversion on such blocks, M units of independent real number data (DFT coefficient data or DCT coefficient data) are obtained. The M units of real number data thus obtained are quantized and coded, thus generating coded data.
In decoding the coded data to reproduce regenerative waveform signals, the coded data are decoded and inversely quantized, and inverse spectral conversion by inverse DFT or inverse DCT is carried out on each block of the resultant real number data corresponding to the block at the time of coding, thus generating waveform element signals. Then, blocks consisting of the waveform element signals are connected to reproduce waveform signals.
In the regenerative waveform signals thus obtained, a connection distortion in connecting the blocks remains, which is less desirable in terms of the auditory sense. Thus, in order to reduce the connection distortion between the blocks, in carrying out spectral conversion using DFT or DCT in actual coding, M1 units of sample data each of the adjacent blocks are caused to overlap each other for spectral conversion.
However, in the case where M1 units of sample data each of the adjacent blocks are caused to overlap each other for spectral conversion, M units of real number data are obtained with respect to (Mxe2x88x92M1) units of sample data on the average, and the number of real number data obtained by spectral conversion becomes greater than the number of original sample data actually used for spectral conversion. Since these real number data are subsequently quantized and coded, the increase in the number of real number data obtained by spectral conversion with respect to the original sample data is less desirable in terms of coding efficiency.
On the contrary, in the case where the above-described MDCT is used similarly as the method for spectral conversion of waveform signals consisting of sample data such as digital audio signals, in order to reduce the connection distortion between the blocks, spectral conversion is carried out by using 2M units of sample data obtained by causing M units of sample data each of the adjacent blocks to overlap each other, and M units of independent real number data (MDCT coefficient data) are obtained. Thus, in this spectral conversion using MDCT, M units of real number data are obtained with respect to M units of sample data on the average, and coding can be carried out at a higher efficiency than in the above-described case of spectral conversion using DFT or DCT.
In decoding the coded data obtained by quantizing and coding the real number data obtained by the spectral conversion using MDCT so as to generate regenerative waveform signals, the coded data are decoded and inversely quantized, and inverse spectral conversion by inverse MDCT is carried out on the resultant real number data to obtain waveform elements in the block. Then, the waveform elements in the block are added while being caused to interfere with each other, thus reconstituting waveform signals.
FIG. 1 is a block diagram showing an exemplary structure of a conventional information coding device for coding acoustic waveform signals. Waveform signals inputted from an input terminal are split into, for example, four bands by a band splitting filter 121 employing the above-described polyphase quadrature filter. The signals of the four bands split by the band splitting filter 121 are sent to corresponding spectral conversion circuits 122-1 to 122-4, respectively. The signals of the respective bands inputted to the spectral conversion circuits 122-1 to 122-4 are converted to corresponding signal frequency components, and are then supplied to a quantization precision determination circuit 123 and a normalization/quantization circuit 124. The normalization/quantization circuit 124 carries out normalization and quantization by using quantization precision information found by the quantization precision determination circuit 123.
The normalization/quantization circuit 124 supplies normalized coefficient information consisting of normalized coefficients at the time normalization and coded signal frequency components to a code string generation circuit 125. The code string generation circuit 125 generates a code string from the quantization precision information inputted from the quantization precision determination circuit 123 and the normalized coefficient information and the coded signal frequency components inputted from the normalization/quantization circuit 124, and outputs the generated code string.
FIG. 2 is a block diagram showing a specific exemplary structure of an information decoding device for decoding the code string generated by the information coding device of FIG. 1 so as to generate and output acoustic signals.
A code string resolution circuit 131 extracts, from an inputted code string (code string generated by the information coding device of FIG. 1), information and components corresponding to the normalized coefficient information and the signal frequency components outputted from the normalization/quantization circuit 124 of FIG. 1 and information corresponding to the quantization precision information outputted from the quantization precision determination circuit 123, and outputs the extracted information and components to a signal component decoding circuit 132.
The signal component decoding circuit 132 restores, from the information and components, the respective signal frequency components outputted from the spectral conversion circuits 122-q to 122-4 of FIG. 1, and supplies the signal frequency components to corresponding inverse spectral conversion circuits 133-1 to 133-4, respectively. The inverse spectral conversion circuits 133-1 to 133-4 carry out inverse spectral conversion processing corresponding to the spectral conversion circuits 122-1 to 122-4, respectively, and supply the resultant band signals to a band synthesis filter 134 corresponding to the band splitting filter 121 of FIG. 1. As the band synthesis filter 134, for example, an inverse polyphase quadrature filter (IPQF) is used. The band synthesis filter 134 generates acoustic waveform signals from the signals of four bands supplied from the inverse spectral conversion circuits 133-1 to 133-4, and outputs the acoustic waveform signals.
A method for coding in the information coding device of FIG. 1 will now be described with reference to FIG. 3.
Spectral signal components ES shown in FIG. 3 are obtained by converting input acoustic waveform signals to a total of 64 spectral signal components ES for each predetermined time frame, by the spectral conversion circuits 122-1 to 122-4 of FIG. 1. These 64 spectral signal components ES are gathered in groups (referred to as coding units) by five predetermined bands (bands b1 to b5), and are then normalized and quantized by the normalization/quantization circuit 124. In this case, the bandwidth of the coding units is set to be narrower on the lower frequency side and to be broader on the higher frequency side so that generation of quantization noise can be controlled in accordance with auditory characteristics. In FIG. 3, the levels of absolute values of spectral signals (frequency components) obtained by MDCT processing are converted to dB values, and the normalized coefficient values of the respective coding units are also shown.
In the information coding device of FIG. 1 for coding information in this manner, the scale of the coding device can be reduced by using, for example, only the spectral conversion circuit 122-1 for coding only a desired band without using the other spectral conversion circuits 122-2 to 122-4. Also, if all the information regions used for coding all the bands are used in coding a desired band, the sound quality of the desired band can be improved.
FIG. 4 is a block diagram showing a specific exemplary structure of an information coding device having its hardware scale reduced by carrying out spectral conversion of only the lowest frequency band. In this case, spectral conversion is carried out only on the lowest frequency band. However, as a matter of course, it is possible to carry out spectral conversion only on another arbitrary frequency band.
In FIG. 4, the same circuit components as those of the information coding device of FIG. 1 are denoted by the same numerals and therefore will not be described further in detail. In this information coding device, only the signal frequency component of the lowest frequency band, of the four bands split by the band splitting filter 121, is sent to the spectral conversion circuit 122-1. The other signal frequency components are not used because spectral conversion is not carried out on these signal frequency components. The spectral conversion circuit 122-1 spectrally converts the inputted signal of the predetermined lowest band to a signal frequency component, and supplies the signal frequency component to the quantization precision determination circuit 123 and the normalization/quantization circuit 124. The normalization/quantization circuit 124 carries out normalization and quantization by using quantization precision information found by the quantization precision determination circuit 123.
Although FIG. 4 shows the example in which only the single spectral conversion circuit 122-1 is used, an information coding device using two or three spectral conversion circuits can be similarly realized.
FIG. 5 shows an example of a code string generated by the information coding device of FIGS. 1 or 4. The coding unit information U1 to U5 of this code string is constituted by quantization precision information, normalized coefficient information, and normalized and quantized signal component information SC1 to SC8. The code string is recorded onto a recording medium such as a magneto-optical disc or transmitted through a transmission medium such as a network.
In the coding unit information U1, the quantization precision of the corresponding coding unit is two bits, indicating that eight spectral signal components are included in this coding unit. If the quantization precision information is 0 (zero) as in the coding unit information U4, it is indicated that coding is not actually carried out in this coding unit.
In the information decoding device of FIG. 2 for decoding a code string, the hardware scale required for the information decoding device can be reduced by using, for example, only the inverse spectral conversion circuit 133-1 for outputting only the signal frequency components including a desired band without using the other inverse spectral conversion circuits 133-2 to 133-4.
FIG. 6 is a block diagram showing a specific exemplary structure of an information decoding device having its hardware scale reduced by carrying out inverse spectral conversion of only the lowest frequency band. In this case, inverse spectral conversion is carried out only on the lowest frequency band. However, as a matter of course, it is possible to carry out inverse spectral conversion only on another arbitrary frequency band.
In FIG. 6, the same portions as those of the information decoding device of FIG. 2 are denoted by the same numerals and therefore will not be described further in detail. Of the signal frequency components decoded by the signal component decoding circuit 132, only the signal frequency component of the lowest frequency band is sent to the inverse spectral conversion circuit 133-1. The other signal frequency components are not used because the inverse spectral conversion is not carried out on these signal frequency components. The inverse spectral conversion circuit 133-1 carries out inverse spectral conversion of the signal frequency component of the predetermined lowest band, and supplies the resultant band signal to the band synthesis filter 134. The band synthesis filter 134 generates output acoustic signals from the band signal from the inverse spectral conversion circuit 133-1 and band signals having a value 0 inputted from terminals 101 to 103, and outputs the output acoustic signals.
In the information decoding device of such structure, by selecting the reproducing band, it suffices to use only the single inverse spectral conversion circuit 133-1 as shown in FIG. 6, while the four inverse spectral conversion circuits 133-1 to 133-4 are required in the decoding device of FIG. 2. Thus, the hardware scale of the decoding device can be diminished and the cost can also be reduced.
Although FIG. 6 shows the example in which only the single inverse spectral conversion circuit is used, an information decoding device using two or three inverse spectral conversion circuits can be similarly realized.
Meanwhile, in the case where the code string generated by the information coding device of FIG. 4 is decoded by using the information decoding device of FIG. 2, or in the case where the code string generated by the information coding device of FIG. 1 is decoded by using the information decoding device of FIG. 6, the aliasing component generated by the characteristics of the band splitting filter 121 or the band synthesis filter 134 is not cancelled but is included in the output acoustic signals, thus raising a problem of deterioration in sound quality.
This problem will now be described using specific examples. FIG. 7 shows frequency characteristics in the case where the above-described polyphase quadrature filter of quadrisection is used as the band splitting filter 121. The lateral axis represents the frequency, and 6 kHz, 12 kHz and 18 kHz scaled on the lateral axis represent the split frequencies in the case where the sampling frequency is 48 kHz. Overlapping of the characteristics of the filter is generated in a frequency region of a predetermined width around the split frequency as the center, and the signals of that region are included in the output of the filter, as the aliasing components, which are frequency signals symmetrical with respect to the split frequency, with the magnitude of amplitude corresponding to the cut-off characteristics of the filter. In the vicinity of the split frequency of 6 kHz, a region from 5 kHz to 7 kHz is a region where the filter characteristics overlap.
FIG. 8 shows the state of an aliasing component generated in the case where signal components exist in the vicinity of the split frequency of 6 kHz. An aliasing component B, corresponding to an original signal A which is a frequency signal component exceeding 6 kHz in the above-described region where the filter characteristics overlap, appears in the frequency band not higher than 6 kHz.
In general, this aliasing component B is cancelled by the original signal A in decoding. Similarly, an aliasing component appears in the frequency band exceeding 6 kHz, but this aliasing component is cancelled by the original signal in decoding.
However, in the case where the code string generated by the information coding device of FIG. 4 is decoded by the information decoding device of FIG. 2, the frequency component not lower than 6 kHz does not exist, and therefore the aliasing component not higher than 6 kHz cannot be cancelled in the band synthesis filter 134. Also, the signal for cancelling the aliasing component by the original signal not higher than 6 kHz appears as a signal component not lower than 6 kHz.
In the information decoding device of FIG. 6, since inverse spectral conversion processing using the inverse spectral conversion circuit is not carried out with respect to the frequency not lower than 6 kHz, the original signal not lower than 6 kHz does not exist and the aliasing component not higher than 6 kHz is not cancelled in the band synthesis filter 134. Also, the signal for cancelling the aliasing component by the original signal not higher than 6 kHz appears as a signal component not lower than 6 kHz.
The signal thus generated appears in the output acoustic signals, depending on the frequency signal component of the original signal. Therefore, the demodulated acoustics signals are heard as unpleasant sounds.
In view of the foregoing status of the art, it is an object of the present invention to enable restraint of deterioration in sound quality at the time of coding and decoding only a part of frequency bands of waveform signals split into a plurality of frequency bands.
An information decoding method according to the present invention is adapted for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The method includes: selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; in the first frequency band, band-limiting a signal component in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal component in the first frequency band.
An information decoding device according to the present invention is adapted for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The device includes: means for selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; means for band-limiting, in the first frequency band, a signal component in a frequency filtering overlap region between the first frequency band and the second frequency band; and means for inversely converting the band-limited signal component in the first frequency band.
In the information decoding method and the information decoding device, when decoding a signal of at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of frequency bands, the value of a signal component of a band adjacent to a band not be decoded, of the bands to be decoded, is limited.
A providing medium according to the present invention is adapted for providing processing for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The processing includes: selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; in the first frequency band, band-limiting a signal component in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal component in the first frequency band.
An information decoding method according to the present invention is adapted for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The method includes: identifying that the first frequency band is encoded and the second frequency band is not encoded; in the first frequency band, band-limiting a signal component in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal component in the first frequency band.
An information decoding device according to the present invention is adapted for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The device includes: means for identifying that the first frequency band is encoded and the second frequency band is not encoded; means for band-limiting, in the first frequency band, a signal component in a filtering frequency overlap region between the first frequency band and the second frequency band; and means for inversely converting the band-limited signal component in the first frequency band.
A providing medium according to the present invention is adapted for providing processing for decoding a signal comprising at least one frequency band from a code string obtained by converting and coding a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The processing includes: identifying that the first frequency band is encoded and the second frequency band is not encoded; in the first frequency band, band-limiting a signal component in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal component in the first frequency band.
An information decoding method according to the present invention is adapted for decoding a code string obtained by converting and coding at least one band of a signal split into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band. The method includes: selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal component of the first frequency band.
An information decoding device according to the present invention is adapted for decoding a code string obtained by converting and coding at least one band of a signal split into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band. The device includes: means for selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; means for band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band; and means for inversely converting the band-limited signal component of the first frequency band.
A providing medium according to the present invention is adapted for providing processing for decoding a code string obtained by converting and coding at least one band of a signal split into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band. The processing includes: selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band; and inversely converting the band-limited signal of the first frequency band.
An information decoding method according to the present invention is adapted for decoding a code string obtained by coding at least one frequency band of a signal split into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band. The method includes: in the first frequency band, restoring frequency signal components from the code string; and inversely converting the restored frequency signal components; where the inverse frequency conversion step includes limiting the value of a signal component existing in a frequency overlap region between the first frequency band and the second frequency band.
An information decoding device according to the present invention is adapted for decoding a code string obtained by coding at least one frequency band of a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The device includes: means for selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; means for restoring, in the first frequency band, frequency signal components from the code string; and means for inversely converting the restored frequency signal components; where the inverse frequency conversion means includes means for limiting the value of a signal component existing in a frequency overlap region between the first frequency band and the second frequency band.
A providing medium according to the present invention is adapted for providing processing for decoding a code string obtained by coding at least one frequency band of a signal split into a plurality of adjacent frequency bands, including a first frequency band adjacent to a second frequency band. The processing includes: selecting the first frequency band as a frequency band to be decoded and selecting the second frequency band as a frequency band not to be decoded; in the first frequency band, restoring frequency signal components from the code string; and inversely converting the restored frequency signal components; where the inverse frequency conversion step includes limiting the value of a signal component existing in a frequency overlap region between the first frequency band and the second frequency band.
An information coding method according to the present invention is adapted for coding an input signal. The method includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; converting the first frequency band to a signal frequency component; band-limiting the signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
An information coding device according to the present invention is adapted for coding an input signal. The device includes: means for splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; means for selecting the first frequency band to be coded; means for selecting the second frequency band not to be coded; means for converting the first frequency band to a signal frequency component; means for band-limiting the signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
A providing medium according to the present invention is adapted for providing processing for coding an input signal. The processing includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; converting the first frequency band to a signal frequency component; band-limiting the signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
An information coding method according to the present invention is adapted for coding an input signal. The method includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; converting a time signal of the first frequency to frequency signal components and coding the frequency signal components; and generating a code string from the coded signal; where converting the time signal includes band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
An information coding device according to the present invention is adapted for coding an input signal. The device includes: means for splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; means for converting a time signal of the first frequency to frequency signal components and coding the frequency signal components; and means for generating a code string from the coded signal; where the converting means includes means for band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
A providing medium according to the present invention is adapted for providing processing for coding an input signal. The processing includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; converting a time signal of the first frequency to frequency signal components and coding the frequency signal components; and generating a code string from the coded signal; where converting the time signal includes band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.
A providing medium according to the present invention is adapted for providing a signal coded by an information coding method for coding an input signal. The information coding method includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band; and converting the band-limited signal.
A providing medium according to the present invention is adapted for providing a signal coded by an information coding method for coding an input signal. The information coding method includes: splitting the input signal into a plurality of frequency bands, including a first frequency band adjacent to a second frequency band; selecting the first frequency band to be coded; selecting the second frequency band not to be coded; converting a time signal of the first frequency to frequency signal components and coding the frequency signal components; and generating a code string from the coded signal; wherein converting the time signal includes band-limiting a signal component of the first frequency band in a filtering frequency overlap region between the first frequency band and the second frequency band.